1. Field of the Invention
The invention is related to the field of electronic fuel control for internal combustion engines and, in particular, the invention is related to the electronic computation of engine fuel requirements during transient modes of operation as determined from the engine speed and pressure in the intake manifold.
2. Prior Art
Fuel delivery to internal combustion engines during transient modes of operation such as acceleration or deceleration has been extensively treated in the prior art. Electronic control units for electronic fuel injection (EFI) equipped engines normally have auxiliary circuits of various types for enriching the fuel mixture during acceleration and decreasing or terminating the fuel delivery during deceleration. Acceleration fuel enrichment circuit, such as disclosed by R. W. Rothfuse and J. R. Nagy U.S. Pat. No. 3,749,065), generates a first fuel enrichment signal operative to inject a predetermined quantity of fuel into the engine immediately upon the receipt of an acceleration command independent of the injection signals generated by the electronic control unit. In addition to the first enrichment signal, the enrichment circuit also increased the duration of the injection pulses generated by the electronic control unit. Injection pulses with increased duration are generated as long as a signal indicative of the acceleration command exists. Rachel, in U.S. Pat. No. 3,720,191, teaches a similar system in which the increased length of the injection pulses generated by the electronic control unit is dependent upon the magnitude and duration of the demanded acceleration derived from a potentiometer mechanically linked to the throttle mechanism. The added increment to the injection pulses exponentially decays after the demand for acceleration is terminated. Long, in U.S. Pat. No. 3,548,791, teaches an acceleration enrichment circuit in which the signal indicative of a demand for acceleration is a pressure change in the intake manifold. In the Long system the demand for acceleration changes a mode of operation of the electronic control unit which, in response to an acceleration demand, produces additional enrichment fuel injection pulses at a rate equal to a firing rate of the cylinders. The duration of these additional acceleration pulses is fixed and the number of pulses is dependent upon the magnitude of the acceleration signal. Ono et al, in U.S. Pat. No. 3,673,989, teaches two acceleration enrichment circuits. The first circuit is triggered by a differentiator circuit responding to the change in pressure in the intake manifold and generates, at a predetermined frequency, a series of injection pulses having fixed pulse widths. The second circuit integrates the acceleration signal and provides a bias signal to the electronic control unit which extends the length of the injection pulses for a fixed period of time. Kazuo Shinoda et al, in U.S. Pat. No. 3,719,176, teaches an acceleration enrichment circuit in which an acceleration signal derived from the intake manifold pressure is integrated to modify the duration of the injection pulses generated by the electronic control unit. The integrated pressure signal is applied to a pulse width modification circuit which generates primary pulses which decay during the decay time of the integration circuit.
The above described patents are indicative of the state of the art of the techniques used for fuel enrichment during acceleration periods. The reading of prior art reveals that acceleration fuel enrichment and deceleration fuel curtailment has been treated empirically by those skilled in the art. The present invention relates to an electronic fuel control system in which the engine's fuel requirements are computed in accordance with the actual air flow to the engine derived from both static and dynamic measurements of the pressure in the engine's air intake manifold. By utilizing both the dynamic and static components of the pressure in the intake manifold, the fuel enrichment for acceleration or fuel leaning for deceleration are computed on the basis of actual air flow. The dynamic component of the pressure signal provides a first order correction to the computed fuel requirements during the transient modes of operation. Empirical corrections such as made in the prior art are then relegated to a secondary type of correction which corrects for such things as wall wetting, engine and air temperatures and other factors not associated with the air flow to the engine.